Staling of baked products, principally bread, has been ascribed to certain properties of the starch component of flour. Starch is essentially composed of amylose forming the core of starch granules and amylopectin forming the outer "envelope" of starch granules. Starch suspensions have been observed to retrograde on standing to precipitate the amylose which, by some, has been given as the explanation of the phenomenon of staling. Others have explained staling of bread in terms of the amylopectin chains in starch associating to cause a greater rigidity of the bread crumb which is characteristic of stale bread.
It is generally recognized to be of some commercial importance to retard the staling of baked products so as to improve their shelf-life. Retardation of the staling process may, for instance, be brought about by the addition of monoglycerides to dough. The antistaling effect of the monoglycerides may partly be ascribed to their ability to bind water and partly to the formation of monoglyceride-amylose complexes wherein the long hydrocarbon chain penetrates into the cavity of the amylose helix and thereby stabilise the helical structure to prevent retrogradation.
Enzymatic retardation of staling by means of .alpha.-amylases has also been described, vide for instance U.S. Pat. No 2,615,810 and U.S. Pat. No. 3,026,205 as well as O. Silberstein, "Heat-Stable Bacterial Alpha-Amylase in Baking", Baker's Digest 38(4), August 1964, pp. 66-70 and 72. The use of .alpha.-amylase for retarding the staling of bread has, however, not become widespread. The reason for this is assumed to be that the medium-molecular weight branched compounds, termed maltodextrins (with 20-100 glucose units in the molecule), generated through the hydrolytic action of .alpha.-amylases have a sticky consistency in themselves resulting in the formation of a sticky or gummy crumb, and consequently an unacceptable mouthfeel, of the baked product if the .alpha.-amylase is overdosed so that the maltodextrins are present in excessive quantities.
It has previously been suggested to remedy the deleterious effects of very large doses of .alpha.-amylase added to dough by adding a debranching enzyme such as pullulanase, cf. U.S. Pat. No. 4,654,216, the contents of which are incorporated herein by reference. The theory behind the addition of a debranching enzyme to obtain an antistaling effect while concomitantly avoiding the risk of producing a gummy crumb in the resulting bread is that by cleaving off the branched chains of the dextrins generated by .alpha.-amylase hydrolysis which cannot be degraded further by the .alpha.-amylase, the starch is converted to oligosaccharides which do not cause gumminess.